HP C/iX Reference Manual (31506-90011)

Chapter 3 29

Data Types and Declarations

Storage-Class Speciﬁers

A storage-class speciﬁer is one of several keywords that determines the duration and

linkage of an object.

Syntax

storage-class

::=

typedef

extern

static

auto

Description

You can use only one storage-class speciﬁer in a declaration.

The typedef keyword is listed as a storage-class speciﬁer because it is syntactically

similar to one.

The keyword extern affects the linkage of a function or object name. If the name has

already been declared in a declaration with ﬁle scope, the linkage will be the same as in

that previous declaration. Otherwise, the name will have external linkage.

The static storage-class speciﬁer may appear in declarations of functions or data objects.

If used in an external declaration (either a function or a data object), static indicates that

the name cannot be referenced by other translation units. Using the static storage class

in this way allows translation units to have collections of local functions and data objects

that are not exported to other translation units at link time.

If the static storage class is used in a declaration within a function, the value of the

variable is preserved between invocations of that function.

The auto storage-class speciﬁer is permitted only in the declarations of objects within

blocks. An automatic variable is one that exists only while its enclosing block is being

executed. Variables declared with the auto storage-class are all allocated when a function

is entered. Auto variables that have initializers are initialized when their deﬁning block is

entered normally. This means that auto variables with initializers are not initialized when

their declaring block is not entered through the top.

The register storage class suggests that the compiler store the variable in a register, if

possible. You cannot apply the & (address-of) operator to register variables.

If no storage class is speciﬁed and the declaration appears in a block, the compiler defaults

the storage duration for an object to automatic. If the declaration of an identiﬁer for a

function has no storage-class speciﬁer, its linkage is determined exactly as if it were

declared with the extern storage-class speciﬁer.

If no storage class is speciﬁed and the declaration appears outside of a function, the

compiler treats it as an externally visible object with static duration.